Occami Shell

It is free software inspired by bash that aims to be a command line interpreter for interactive development environments in POSIX systems.

Occam's Razor is the philosophy that guides development and decision-making in the face of conflicts, keeping only the features most used by developers and, in the case of multiple solutions, choosing the simplest.

The initiative also serves as a laboratory to train software engineering techniques—unit tests, integration tests, teamwork, asynchronous communication, code versioning, automated test routines, etc.

This shell has the following features:

• Display a prompt when waiting for a new command.

• Have a working history.

• Search and launch the right executable (based on the PATH variable or using a relative or an absolute path).

• Avoid using more than one global variable to indicate a received signal. Consider the implications: this approach ensures that your signal handler will not access your main data strucutures.

• Not interpret unclosed quotes or special characters which are not required by the subject as \ (backslash) or ; (semicolon).

• Handle ' (single quote) which should prevent the shell from interpreting the metacharacters in the quoted sequence.

• Handle " (double quote) which should prevent the shell from interpreting the metacharacters in the quoted sequence except for $ (dollar sign).

• Implement redirections:

  • '<' should redirect input.
  • '>' should redirect output.
  • '<<' should be given a delimiter, then read the input until a line containing the delimiter is seen. However, it doesn't have to update the history!
  • '>>' should redict output in append mode.

• Implement pipes (| character). The output of each command in the pipeline is connected to the input of the next command via a pipe.

• Handle environment variables ($ followed by a sequence of characters) which should expand their values.

• Handle $? which should expand to the exit status of the most recently executed foreground pipeline.

• Handle ctrl-C, ctrl-D and ctrl-\ which should behave like in bash.

• In interactive mode:

  • ctrl-C displays a new prompt on a new line.
  • ctrl-D exits the shell.
  • ctrl-\ does nothing.

• Implement the following builtins:

  • echo with option -n
  • cd with only a relative or absolute path
  • pwd with no options
  • export with no options
  • unset with no options
  • env with no options
  • exit with no options

References

1. 42 Network. (2023). Minishell - As beautiful as a shell, Version 7.1 [PDF file]. https://projects.intra.42.fr/projects/42cursus-minishell. (Accessed March 4, 2024)

2. Free Software Foundation. (2022). GNU Bash manual. https://www.gnu.org/savannah-checkouts/gnu/bash/manual/. (Accessed March 4, 2024)

3. The Open Group. (2018). The Open Group Base Specifications Issue 7, 2018 edition. https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/. (Accessed March 4, 2024)